We propose to continue to perfect analytical methods for the detection and identification of oxidation products of cholesterol, 5 alpha-cholest-7-en-3 beta-ol, and 5 alpha-lanost-8-en-3-beta-ol under conditions likely to be found in tissues exposed to polluted air containing active oxygen species as oxidants. We specifically seek to identify oxidation products of these sterols which are formed from reaction with singlet molecular oxygen. The proposed work will emphasize the application of high performance liquid column chromatography with associated chemical ionization mass spectrometry and other spectral methods.